Field of the Invention
The present invention relates to a method for preparing a membrane lined with a layer of a gel and a frame for supporting such a membrane, which frame is designed for the implementation of this method. More particularly, the invention relates to the making up of a gel/membrane assembly which can be used in a technique for separating macromolecules by electrophoresis.
In such a technique a layer of a gel such as agarose or a polyacrylamide and an electric field established between two opposite edges of the layer are used. Samples of macromolecules, for example macromolecules of nucleic acid, to be separated are deposited in wells formed in the gel along one of these two edges of the layer. The assembly is next immersed in a suitable electrophoresis liquid. Under the effect of the electric field, the macromolecules of the samples housed in the wells move towards the opposite edge of the layer, through the gel, at rates which depend notably on their molecular mass, so that at the end of a given time, macromolecules of different molecular masses have traveled different distances into the gel.
The macromolecules thus separated are next transferred, either by fluid entrainment or by means of an electric field applied perpendicular to the gel layer, onto a membrane placed against one face of this layer, with a view to their subsequent hybridization and to their subsequent detection. A method and an electrophoresis device, which are designed for achieving such a controlled migration of macromolecules in a stack of rectangular plates of gel, is described in European Patent Application Publication No. 358,556.
When a membrane is used f or supporting the gel layer, the making-up of the gel/membrane assembly is particularly tricky on account of the fineness and of the lack of stiffness of the membrane used, commonly a thin sheet of nitrocellulose, optionally filled with nylon in order to increase its mechanical strength.
Known frames for supporting such a membrane have the drawback of not enabling this membrane to be held in a plane under uniform tension. Pleats resulting f rom tension defects then form in the membrane. The gel layer which is cast onto a membrane thus pleated has deformations which oppose a steady progression of the macromolecules in the layer and render the result of the migration useless. The elimination of these pleats requires lengthy and fastidious manipulations which are incompatible with the requirements of an automated, or indeed industrial, manufacture.